In recent years, there has been a demand for inexpensive formation of metallic electrodes, which are used for solder joint or the like, on a circuit surface formed on a semiconductor substrate.
In response to the demand, as a technology for forming metallic electrodes without the necessity of including a photolithography step in patterning, a patent document 1 (JP-A-2006-186304) has disclosed a technology for forming metallic electrodes that is implemented in a process of fabricating a semiconductor device in which: bed electrodes are formed on one side of a semiconductor substrate; a protective film is formed on the bed electrodes and openings are formed in the protective film; and metallic electrodes for connections are formed on the surfaces of the bed electrodes bared through the openings. According to the technology, a level difference which is created so that the surfaces of the bed electrodes bared through the openings will recede from the top of the protective film is utilized in order to pattern a metallic film formed on the bed electrodes and protective film alike through cutting work. Thus, the metallic electrodes are formed.
Like the foregoing technology, when a pattern of metallic electrodes is formed through cutting, cutting work has to be achieved with such high precision that a variance in a magnitude of cutting with the surface of a metallic film as a reference will fall below, for example, 2 μm all over the surface of a semiconductor substrate.
Herein, when the semiconductor substrate is adsorbed or secured to an adsorption stage, the semiconductor substrate is deformed in order to flatten the back side of the semiconductor substrate. Consequently, the principal side of the semiconductor substrate is shaped to have large irregularities while reflecting the original irregular shape of the back side thereof.
Cutting work is performed on a plane parallel to the adsorption stage. Therefore, when the semiconductor substrate has a variance in the thickness, which is larger than a requested degree of precision in the magnitude of cutting, for example, 3 μm, an area where the requested degree of precision in the magnitude of cutting is not satisfied is present in part of the plane. This poses a problem in that a product yield is degraded.
Accordingly, it is required to realize a metallic electrode forming method for semiconductor devices in which metallic electrodes are formed on a semiconductor substrate, which has a variance in the thickness thereof that is larger than a requested degree of precision in a magnitude of cutting, by patterning a metallic film through cutting work that is performed to satisfy the requested degree of precision in the magnitude of cutting, and a semiconductor device.
Further, like the foregoing technology, when a pattern of metallic electrodes is formed through cutting, an area where a metallic film is layered on a protective film made of a resin material has to be cut. When the surface roughness of the protective film intensifies, a dielectric strength decreases. Therefore, the surface roughness of the protective film having undergone cutting work has to be restricted to 100 nm or less.
Since the metallic film and protective film are greatly different from each other in terms of rigidity, when the area where the metallic film is layered on the protective film is cut, a tensile stress that reacts on the protective film gets higher in the vicinity of the tip of a cutting jig. Consequently, the work side of the protective film that is the underlying film of the metallic film is plucked. This poses a problem in that the surface roughness of the protective film having undergone cutting work is intensified.
Accordingly, it is required to realize a metallic electrode forming method for semiconductor devices capable of diminishing the surface roughness of a protective film having undergone cutting work.